Production of paraffinic dinitriles, dicarboxamides or dicarboxylates by electrolytic hydrodimerization of an alpha, beta-olefinic nitrile, carboxamide or carboxylate is well known, e.g. from U.S. Pat. Nos. 3,193,475-79 and 3,193,481-83 issued July 6, 1965, to M. M. Baizer. Although the process has been sufficiently attractive that it has been in commerical use for over nine years, efforts to develop improvements thereon have been continued with particular emphasis on lowering electric power costs and mitigating electrode corrosion and fouling tendencies because of which it has been heretofore commercially preferable to carry out the process with a cell-dividing membrane.
With the object of maintaining high electrolyte conductivity while employing an electrolysis medium containing organic salts in a proportion small enough for attractive use of a single-compartment (membraneless) cell, one approach to improvement of the process has been to use as the electrolysis medium an aqueous solution of a mixture of quaternary ammonium and alkali metal salts together with the olefinic compound to be hydrodimerized. An example of such an approach is described in Netherlands Patent Application No. 66,10378 laid open for public inspection Jan. 24, 1967, and further development thereof is described in U.S. Pat. No. 3,616,321 issued Oct. 26, 1971, to A. Verheyden et al. and U.S. Pat. No. 3,689,382 issued Sept. 5, 1972, to H. N. Fox et al. However, all known variations of the process are characterized by some degree of inefficiency in use of the electrolyzing current, and this problem is typically even more significant in those process variations that utilize such an undivided cell.
For example, not all of the electroreduction that occurs at the cell cathode takes the form of the desired hydrodimerization reaction or even the generally undesired simple hydrogenation of the olefinic starting material. Instead, a minor but significant proportion normally results in generation of molecular hydrogen. This hydrogen ordinarily accumulates in the electrolysis offgas together with oxygen produced at the anode and, in fact, the proportion of hydrogen in the offgas is a fairly accurate indicator of the proportion of consumed electrolysis current that was wasted on such hydrogen production. At relatively low concentrations of hydrogen in the offgas, the percentage by volume of hyrogen in the offgas is generally about twice the percentage of current consumed in the electrolysis by undesired production of molecular hydrogen. More specifically, the percentage of current consumed in the electrolysis by undesired production of molecular hydrogen is normally equal to fifty times the percentage by volume of hydrogen in the offgas divided by one hundred less the percentage by volume of hydrogen in the offgas, i.e., 50 .times. %H.sub.2 /(100-%H.sub.2). For example, a concentration of 10% by volume of hydrogen in an electrolysis offgas usually indicates that about 5.5% of the current consumed in the electrolysis was wasted on molecular hydrogen production and, accordingly, that the current efficiency of the hydrodimerization process was not possibly any greater than about 94.5%.
Clearly, the higher the proportion of the electrolyzing current that produces molecular hydrogen rather than the desired hydrodimer, the greater the cost of production of the hydrodimer will be. Accordingly, a process improvement whereby an olefinic compound from the aforementioned class can be electrolytically hydrodimerized with a resultingly lowered production of molecular hydrogen and a thereby increased current efficiency is highly desirable, and it is an object of this invention to provide such an improvement. Additional objects of the invention will be apparent from the following description and Examples in which all percentages are by weight except where otherwise noted.